A buck regulator may be used to generate a regulated output voltage than is less than the input voltage; conversely, a boost converter may be used to generate a regulated output voltage that is greater than the input voltage. However, DC-DC converters with step up/step down characteristics need to be used when the input and output voltage ranges overlap. Several different topologies may be used, such as SEPIC, Cuk, a one-mode buck/boost regulator, a three-mode buck/boost regulator, and the like. However, these topologies are inferior to both boost and buck regulation for efficiency and other reasons. A one mode buck/boost regulator operates in buck/boost mode only. A three-mode buck/boost regulator operates in three modes. If the input voltage is significantly greater than the output voltage, the three-mode buck/boost regulator operates in buck mode. If the input voltage is significantly less than the output voltage, the three-mode buck/boost regulator operates in boost mode. If the input voltage and the output voltage are relatively close to each other, it operates in buck/boost mode. In a typical buck/boost topology, in buck/boost mode the boost switches and the buck switches are switching during the same cycle. However, buck/boost mode is inferior to buck mode or boost mode in terms of efficiency and other performance parameters.
A buck-or-boost (BOB) PFM regulator operates in two modes: boost mode or buck mode. Typically, in a BOB PFM regulator, the input voltage is compared to the desired output voltage, and the circuit operates in either buck mode or boost mode depending on the result of the comparison. However, conventional BOB regulators typically have large output ripple and glitches when changing from buck mode to boost mode or vice versa.